This invention concerns vision correction and, in particular, annular mask contact lenses and related methodology.
Contact lenses are commonplace today. Most individuals with minor vision ailments can quickly acquire and use these lenses in place of prescription eye glasses. This is not true, however, for individuals stricken with poor vision or even for those presbyopic persons requiring bifocal glasses. These individuals are left with little choice in selecting contact lenses; and the lenses which are available typically encumber these patients with other difficulties. For example, presbyopic individuals can opt for bifocal contact lenses, but usually find it difficult to maintain focus during eye movement, or only see clearly at one viewing distance.
The long felt need to develop more versatile lenses has led designers to pinhole contact lenses. These lenses endeavor to utilize the known theories of pinhole imaging, commonly understood in optics as a method to reduce geometrical aberrations, e.g., astigmatism, spherical aberration, and coma. By restricting a person's vision to a small "pinhole" aperture, visual deficiencies are greatly reduced or effectively removed. Unfortunately, the utility of this technology has been diluted because of designs and approaches inappropriate for corrective optometry. For upwards of 50 years pinhole contact lenses have been under consideration, yet they remain today commercially unsuccessful and largely unavailable. As a result, patients afflicted with relatively poor vision are typically unaided by contact lenses.
"Multiple Focal Contact Lenses", as described in U.S. Pat. No. 3,794,414, was one attempt to develop small-aperture contact lenses. This approach combined a pinhole-like aperture with radial slits and scalloped masking regions on a contact lens to supposedly correct both peripheral vision and the effects related to decentered contact lenses. The disclosed designs though, i.e., the use of scalloped patterns and radial slits, actually encourage diffraction effects at the retina. This reduces image quality. The very nature of small-aperture correction is to correct geometrical aberrations in excess of diffraction. Therefore, the benefits achieved according to that patent by incorporating the small, pinhole-like, aperture are likely offset by undesirable diffraction effects.
In addition, the teachings presented in the aforementioned patent do not generally consider the normal functioning of the human pupil. The single largest drawback in pinhole imaging is energy starvation. Small-aperture lenses improve image quality, but at the same time block significant amounts of light energy from reaching the retina. Under dim lighting conditions, a human pupil normally dilates. Without proper consideration, a small-aperture contact would equivalently place a person into darkness, even though the lighting is only dim or low.
Pinhole correction together with the normal functioning of the human pupil is considered in U.S. Pat. No. 4,955,904, which presents an intraocular lens surgically implanted within the eye. The patent, entitled "Masked Intraocular Lens and Method for Treating a Patient With Cataracts", affords cataract patients some form of vision correction through surgery. The intraocular lens is masked to form a pinhole that accommodates the function of the human pupil under different lighting conditions. But, intraocular lenses have operational and other drawbacks. They are not contact lenses; surgery is required and the lens must be permanently implanted with precision through the use of man-made loops. Furthermore, because of material requirements for implantation, these impenetrable lenses can transmit little or no oxygen, a feature widely available in contact lenses. Contact lenses, in addition, are conveniently installed and removed by the patient, and are held in place on the eye through tear tension.
With this background, an object of this invention is to provide an improved small-aperture contact lens, and in particular, one which considers the normal function of the human pupil.
Another object of this invention is to present a contact lens which provides functional imaging during both bright and dim lighting conditions, and over a wide range of viewing distances.
Yet another object of this invention is to provide a small-aperture contact lens and related methodology to selectively block highly aberrated portions of the eye.
Other objects of the invention are evident in the description that follows.